OSLO (Reuters) - About 130 governments meet in Spain next week to agree a stark guide to the mounting risks of climate change that the United Nations says will leave no option but tougher action to fix the problem.

The U.N. climate panel, winner of the 2007 Nobel Peace Prize with former U.S. Vice President Al Gore, will meet in Valencia from November 12-17 to condense 3,000 pages of already published science into a 20-page summary for policy makers.

"There is no reason to question the science any longer," said Achim Steiner, head of the U.N. Environment Programme, who said states should act "in the collective interest of humanity."

"Valencia will add further momentum in the mind of the public around the world that governments ... have no option but to move forward" with tougher policies, he told Reuters on Friday by telephone from Lisbon.

The Intergovernmental Panel on Climate Change (IPCC) comprises both government officials and scientists who will edit and agree a text that draws on work by 2,500 experts to give the most authoritative U.N. overview of global warming since 2001.

He said the world's environment ministers should approve a two-year timetable to work out a successor to the U.N.'s Kyoto Protocol, the main U.N. plan to curb warming until 2012, when they meet on the Indonesian island of Bali next month.

U.N. Secretary-General Ban Ki-moon will attend the final day of the IPCC talks in Valencia.

PEOPLE TO BLAME

Kyoto obliges 36 industrial nations to cut emissions by at least 5 percent below 1990 levels by 2008-12. A new deal would aim to involve outsiders led by the United States and China, the world's top two emitters which have no Kyoto goals.

The draft summary, obtained by Reuters, says global warming is already under way and will be negative overall.

"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level," it starts.

It says there is still time to slow warming, and even the toughest targets for curbing emissions would cost less than 0.12 percent per year of world gross domestic product until 2030.

Environmentalists expressed concern that some governments may seek to water down the IPCC conclusions to stall action. "We must allow scientists to present the unvarnished truth," said Hans Verolme of the WWF conservation group.

Some experts say the IPCC has been conservative in estimates of carbon dioxide emissions or rising sea levels, while a 2007 summer thaw of Arctic sea broke records.

"Some trends are at the upper part of the IPCC projections," said Eystein Jansen of Norway's Bjerknes Centre for Climate Research and an IPCC author.